Semiconductor layer

ABSTRACT

A light-emitting element includes a β-Ga 2 O 3  substrate, a GaN-based semiconductor layer formed on the β-Ga 2 O 3  substrate, and a double-hetero light-emitting layer formed on the GaN-based semiconductor layer.

The present application is a Continuation application of U.S. patentapplication Ser. No. 10/567,369, filed on Feb. 7, 2006, which is basedon and claims priority from International Application No.PCT/JP2004/011531, filed on Aug. 4, 2004, and Japanese PatentApplication No. 2003-290862, filed on Aug. 8, 2003, the entire contentsof which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a semiconductor layer, and moreparticularly to a semiconductor layer in which a GaN system epitaxiallayer having high crystal quality can be obtained.

BACKGROUND ART

FIG. 3 shows a conventional semiconductor layer. This semiconductorlayer includes an Al₂O₃ substrate 11 made of Al₂O₃, an AlN layer 12which is formed on a surface of the Al₂O₃ substrate 11, and a GaN growthlayer 13 which is formed on the AlN layer 12 through epitaxial growth byutilizing an MOCVD (Metal Organic Chemical Vapor Deposition) method(refer to JP 52-36117 B for example).

According to this semiconductor layer, the AlN layer 12 is formedbetween the Al₂O₃ substrate 11 and the GaN growth layer 13, wherebymismatch in lattice constants can be reduced to reduce imperfectcrystalline.

However, according to the conventional semiconductor layer, the latticeconstants of the AlN layer 12 and the GaN growth layer 13 cannot beperfectly made match each other, and thus it is difficult to furtherenhance crystal quality of the GaN growth layer 13. In addition, whenthe conventional semiconductor layer is applied to a light emittingelement, crystalline of a luminous layer is degraded, and luminousefficiency is reduced.

Therefore, an object of the present invention is to provide asemiconductor layer in which a GaN system epitaxial layer having highcrystal quality can be obtained.

DISCLOSURE OF THE INVENTION

In order to attain the above-mentioned object, the present inventionprovides a semiconductor layer characterized by including a first layermade of a Ga₂O₃ system semiconductor, and a second layer obtained byreplacing a part or all of oxygen atoms of the first layer with nitrogenatoms.

According to the semiconductor layer of the present invention, thesecond layer which is obtained by replacing a part or all of the oxygenatoms of the first layer with the nitrogen atoms is formed on the firstlayer made of the Ga₂O₃ system semiconductor, whereby the second layermade of the GaN system compound semiconductor having high crystalline isobtained without interposing a buffer layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a semiconductor layer according toEmbodiment 1 of the present invention;

FIG. 2 is a flow chart showing processes for manufacturing thesemiconductor layer according to Embodiment 1 of the present invention;and

FIG. 3 is a cross sectional view of a conventional semiconductor layer.

BEST MODE FOR CARRYING OUT THE INVENTION

A semiconductor layer according to an embodiment mode of the presentinvention will be described. This embodiment mode is constituted by afirst layer which is made of a Ga₂O₃ system semiconductor, a secondlayer which is made of a GaN system compound semiconductor and which isobtained on the first layer by subjecting a surface of the first layerto nitriding processing or the like to replace a part or all of oxygenatoms of the first layer with nitrogen atoms, and a third layer which ismade of a GaN system epitaxial layer on the second layer. Here, “theGa₂O₃ system semiconductor” contains semiconductors such as Ga₂O₃,(In_(x)Ga_(1-x))₂O₃ where 0≦x<1, (Al_(x)Ga_(1-x))₂O₃ where 0≦x<1, and(In_(x)Al_(y)Ga_(1-x-y))₂O₃ where 0≦x<1, 0≦y<1, and 0≦x+y<1, and alsocontains semiconductors each showing an n-type conductive property or ap-type conductive property through atom replacement or atom defects madefor such a semiconductor. In addition, “the GaN system compoundsemiconductor” and “the GaN system epitaxial layer” containsemiconductors such as GaN, In_(z)Ga_(1-z)N where 0≦z<1, Al_(z)Ga_(1-z)Nwhere 0≦z<1, and In_(z)AlGa_(1-z-p)N where 0≦z<1, 0≦p<1, and 0≦z+p<1,and also contain semiconductors each showing an n-type conductiveproperty or a p-type conductive property through atom replacement oratom defects made for such a semiconductor.

For example, as a first example, the second layer and the third layercan be made of the same compound semiconductor as in the first layermade of Ga₂O₃, the second layer made of GaN, and the third layer made ofGaN. In addition, as a second example, the second layer and the thirdlayer can also be made of different compound semiconductors,respectively, as in the first layer made of made of Ga₂O₃, the secondlayer made of GaN, and the third layer made of In_(z)Ga_(1-z)N where0≦z<1. Also, as a third example, the second layer and the third layercan also be made of different compound semiconductors, respectively, andthe first layer and the second layer can also be made in accordance witha combination different from that in the first example and the secondexample as in the first layer made of (In_(x)Ga_(1-x))₂O₃ where 0≦x<1,the second layer made of In_(z)Al_(p)Ga_(1-z-p)N where 0≦z<1, 0≦p<1, and0≦z+p<1, and the third layer made of Al_(z)Ga_(1-z)N where 0≦z<1.

According to the embodiment mode, since the lattice constants of thesecond layer and the third layer can be made match each other, or can bemade exceedingly approximate to each other, the GaN system epitaxiallayer having high crystal quality is obtained.

Embodiment 1

FIG. 1 shows a semiconductor layer according to Embodiment 1 of thepresent invention. The semiconductor layer of Embodiment 1 includes aβ-Ga₂O₃ substrate 1, as a first layer, which is made of a β-Ga₂O₃ singlecrystal, a GaN layer 2 with about 2 nm thickness, as a second layer,which is formed by subjecting a surface of the β-Ga₂O₃ substrate 1 tonitriding processing, and a GaN growth layer 3, as a third layer, whichis formed on the GaN layer 2 through epitaxial growth by utilizing anMOCVD method for example. Oxygen atoms of the β-Ga₂O₃ substrate 1 arereplaced with nitrogen atoms in the nitriding processing, therebyforming the GaN layer 2.

FIG. 2 shows processes for manufacturing the semiconductor layer.Firstly, the β-Ga₂O₃ substrate 1 is manufactured by utilizing an FZ(floating zone) method (process a). In the first place, a β-Ga₂O₃ seedcrystal and a β-Ga₂O₃ polycrystalline raw material are prepared.

The β-Ga₂O₃ seed crystal is obtained by cutting down a β-Ga₂O₃ singlecrystal through utilization or the like of a cleaved face and has aprismatic shape having a square in cross section, and its axis directionmatches a-axis <100> orientation, b-axis <010> orientation, or c-axis<001> orientation.

For example, powders of Ga₂O₃ with a purity of 4N are filled in a rubbertube, subjected to cold compression at 500 MPa, and sintered at 1500° C.for 10 hours, thereby obtaining the β-Ga₂O₃ polycrystalline rawmaterial.

Next, heads of the β-Ga₂O₃ seed crystal and the β-Ga₂O₃ polycrystallineare made contact each other in ambient of mixed gas of nitrogen andoxygen (changing from 100% nitrogen to 100% oxygen) at a total pressureof 1 to 2 atmospheres in a silica tube, contact portions thereof areheated to be molten, and the dissolved matter of the β-Ga₂O₃polycrystalline is cooled, thereby producing the β-Ga₂O₃ single crystal.When being grown as a crystal in the b-axis <010> orientation, theβ-Ga₂O₃ single crystal has strong cleavage in a (100) face, and hencethe β-Ga₂O₃ single crystal is cut along a face vertical to a faceparallel to the (100) face, thereby manufacturing the β-Ga₂O₃ substrate1. Incidentally, when being grown as a crystal in the a-axis <100>orientation or c-axis <001> orientation, the β-Ga₂O₃ single crystal hasweak cleavage in the (100) face and a (001) face. Hence, theprocessability for all the faces becomes excellent, and thus there is nolimit to the cut face as described above.

Next, the β-Ga₂O₃ substrate 1 is etched by being boiled in a nitric acidsolution at 60° C. (process b). The resulting β-Ga₂O₃ substrate 1 isthen immersed in ethanol and subjected to ultrasonic cleaning (processc). Moreover, after being immersed in water and subjected to theultrasonic cleaning (process d), the β-Ga₂O₃ substrate 1 is dried(process e) and subjected to vacuum cleaning at 1000° C. in a growthchamber of an MOCVD system (process f) to clean a surface of the β-Ga₂O₃substrate 1.

Next, the β-Ga₂O₃ substrate 1 is subjected to nitriding processing(process g). That is to say, the β-Ga₂O₃ substrate 1 is heated for apredetermined period of time in a predetermined ambient atmosphere inthe growth chamber of the MOCVD system. The ambient atmosphere(including the atmosphere), the heating temperature, and the heatingperiod of time are suitably selected, whereby the desired GaN layer 2 isobtained on the surface of the β-Ga₂O₃ substrate 1. For example, theβ-Ga₂O₃ substrate 1 is heated at 1050° C. for 5 minutes in NH₃ ambientat 300 torr, whereby the thin GaN layer 2 with about 2 nm thickness isformed on the surface of the β-Ga₂O₃ substrate 1.

Next, GaN is grown by utilizing the MOCVD method to obtain the GaNgrowth layer 3 (process h). That is to say, when a pressure in thegrowth chamber of the MOCVD system is reduced to 100 torr, and ammoniagas and trimethylgallium (TMG) are supplied as an N supply raw materialand a Ga supply raw material to the growth chamber, respectively, theGaN growth layer 3 with about 100 nm thickness for example grows on theGaN layer 2. The thickness of the GaN growth layer can be controlled byadjusting a concentration of the supply raw materials, the heatingtemperature, and the like.

In Embodiment 1, when trimethylaluminum (TMA) is supplied together withTMG, an AlGaN layer can be formed as the second layer instead of the GaNlayer 2. In addition, when trimethylindium (TMI) is supplied togetherwith TMG, an InGaN layer can be formed as the second layer instead ofthe GaN layer 2.

According to Embodiment 1, the following effects are obtained.

(1) Since the β-Ga₂O₃ substrate 1 having the high crystalline isobtained, the GaN layer 2 formed thereon is obtained which is low inthrough dislocation density and which is high in crystalline. Moreover,since the GaN layer 2 and GaN growth layer 3 match in lattice constantseach other, and also the GaN growth layer 3 grows so as to succeed tothe high crystalline of the GaN layer 2, the GaN growth layer 3 isobtained which is less in through dislocation and which is high incrystalline.

(2) The InGaN layer, for example, is formed between the n-type GaNgrowth layer and the p-type GaN growth layer, whereby it is possible tomanufacture a light emitting element such as a light emitting diode or asemiconductor laser.

(3) Since a luminous layer having high crystalline is obtained when thepresent invention is applied to the light emitting element, luminousefficiency is enhanced.

(4) Since the β-Ga₂O₃ substrate 1 has the conductive property, when thelight emitting element is manufactured, it is possible to adopt avertical type structure in which electrodes are taken out from avertical direction of a layer structure and thus it is possible tosimplify the layer structure and the manufacture process.

(5) Since the β-Ga₂O₃ substrate 1 has a translucent property, light canalso be taken out from the substrate side.

(6) Since the vacuum cleaning (process f), the nitriding processing(process g), and the GaN epitaxial growth (process d) are continuouslyperformed within the growth chamber of the MOCVD system, thesemiconductor layer can be efficiently produced.

At that, InGaN, AlGaN or InGaAlN may also be grown instead of the GaNgrowth layer 3. In the case of InGaN and AlGaN, the lattice constantsthereof can be made nearly match those of the GaN layer 2. In the caseof InAlGaN, the lattice constants thereof can be made match those of theGaN layer 2.

For example, when an Si-doped GaN layer is formed on the thin film GaNlayer 2, a non-doped InGaN layer is formed on the Si-doped GaN layer,and an Mg-doped GaN layer or AlGaN layer is formed on the non-dopedInGaN layer, a double hetero type light emitting element is obtained. Atthis time, when a well layer and a barrier layer which are different inIn composition ratio from each other are alternately formed forformation of the non-doped InGaN layer, a laser diode element having anMQW (multi-quantum well layer) is obtained.

On the other hand, when in FIG. 1, the GaN layer 2 and the substrate 1are removed after the GaN growth layer 3 with a predetermined thicknessgrows, the GaN substrate is obtained. Likewise, an InGaN layer, an AlGaNlayer or an InGaAlN layer is formed instead of the GaN growth layer 3,whereby respective substrates can be obtained.

In addition, while the FZ method has been described as the growingmethod for the β-Ga₂O₃ substrate 1, any other suitable growth methodsuch as an EFG (Edge-defined Film-fed Growth method) method may also beadopted. Also, while the MOCVD method has been described as the growingmethod for the GaN system epitaxial layer, any other suitable growthmethod such as a PLD (Pulsed Laser Deposition) method may also beadopted.

In addition, the semiconductor layer of the present invention is notlimited to the light emitting element, and thus can be applied tovarious kinds of semiconductor components or parts.

INDUSTRIAL APPLICABILITY

According to the semiconductor layer of the present invention, thesecond layer which is obtained by replacing a part or all of the oxygenatoms of the first layer with the nitrogen atoms is formed on the firstlayer made of the β-Ga₂O₃ system semiconductor, whereby the second layerwhich is made of the GaN system compound semiconductor and which has thehigh crystalline is obtained without interposing a buffer layer. Hence,when the GaN system epitaxial layer is formed on the second layer, thelattice constants of the second layer and the GaN system epitaxial layercan be made match each other, or can be made exceedingly approximate toeach other, and thus the GaN system epitaxial layer having the highcrystal quality is obtained.

1. A light-emitting element, comprising: a β-Ga₂O₃ substrate; aGaN-based semiconductor layer formed on the β-Ga₂O₃ substrate; and adouble-hetero light-emitting layer formed on the GaN-based semiconductorlayer.
 2. The light-emitting element according to claim 1, wherein thedouble-hetero light-emitting layer comprises a Si-doped GaN layer, anon-doped InGaN layer formed on the Si-doped GaN layer, and a Mg-dopedGaN layer or a Mg-doped AlGaN layer formed on the non-doped InGaN layer.3. A light-emitting element, comprising: a β-Ga₂O₃ substrate; and amultiple quantum well layer formed on the β-Ga₂O₃ substrate.
 4. Thelight-emitting element according to claim 3, wherein the multiplequantum well layer comprises a well layer as a non-doped InGaN layer anda barrier layer as a non-doped InGaN layer, an In composition ratio ofthe barrier layer being different from that of the well layer.
 5. Amethod of manufacturing a semiconductor substrate, said methodcomprising: forming a GaN-based semiconductor layer on a β-Ga₂O₃substrate; forming a GaN epitaxial layer on the GaN-based semiconductorlayer; and removing the β-Ga₂O₃ substrate and the GaN-basedsemiconductor layer from the GaN epitaxial layer, thereby manufacturinga substrate that comprises the GaN epitaxial layer.
 6. The method ofmanufacturing the semiconductor substrate according to claim 5, whereinthe GaN epitaxial layer comprises a GaN layer, an InGaN layer, an AlGaNlayer, or an InGaAlN layer.